This application claims the priority of 198 21 548.7, filed May 14, 1998, the disclosure of which is expressly incorporated by reference herein.
The invention relates to a method and apparatus for controlling a valve having an electromagnetically operable valve element. When an assigned solenoid is energized by a capturing current pulse, the valve element is moved against an elastic restoring force into a stop-defined end position, reaching the end position at a pertaining impact velocity which is controlled by the variable adjustment of the capturing current pulse.
Valves having an electromagnetically operable valve element are used, for example, as charge cycle valves for internal-combustion engines of motor vehicles. Typically such valves have two oppositely spaced solenoids which operate as switching magnets, one forming an opening magnet and the other forming a closing magnet, and an armature provided on the valve element is movably arranged between pole surfaces of the solenoids. An assigned spring arrangement, usually in the form of two prestressed pressure springs, together with the valve element, forms a spring-ground oscillator, whose rest position is between the two valve end positions. From the rest position, the valve gear is attracted by the closing magnet or by the opening magnet, to move against the elastic restoring force of the spring arrangement into the pertaining end position. Subsequently, the valve is alternately opened and closed by switching off the energizing of the momentarily stopped magnet so that the valve gear is accelerated by the spring arrangement from the previous end position toward the rest position. The valve element moves beyond the rest position, and is then captured by the opposite solenoid against the elastic restoring force of the spring arrangement. For this purpose, it is acted upon by a so-called capturing current pulse. The thus captured valve element will then reach its new, stop-defined end position at an impact velocity which is a function of the capturing current pulse.
Such valves are increasingly important for internal-combustion engines with a variable valve timing, which can achieve a high efficiency, while emissions remain relatively low.
German Published Patent Applications DE 37 33 704 A1 and DE 195 30 394 A1 disclose control methods for such charge cycle valves, in which individual stick times of the armature on the respective solenoids are taken into account, or it is monitored (by detecting the current course and/or voltage course for energizing the solenoid) whether the valve element is being held at rest against its pole surface.
German Published Patent Application DE 196 23 698 A1 discloses a method for controlling such a charge cycle valve as a function of the timing and/or velocity of the impact of the valve element capturing operation. Oscillation signals generated by the valve gear are detected and the valve is controlled as a function of the extent of the detected oscillation signals. In one variation, this method corresponds to the type initially mentioned in that the impact velocity is controlled to ensure secure valve operation on the one hand, and to minimize noise and energy consumption for the valve gear on the other hand, while at the same time, manufacturing tolerances and influences of wear and temperature are compensated. For this purpose, detected vibration signals are used to determine the impact velocity, which is controlled by variable selection of the switch-on time and possibly of the current intensity of the capturing current pulse. Such control is performed by reading desired values from previously stored characteristic diagrams a valve operating mechanism. The desired values thus determined can be modified in the course of the operation, and modified desired values are stored in a characteristic adaptation diagram which can be updated. When a deviation is detected, a correspondingly changed capturing current is set for the next valve operation.
Additional methods and arrangements for valve control with a variable selection of the switch-on point in time of a capturing coil are disclosed in German Published Patent Application DE 195 21 078 A1 and European Published Patent Application EP 0 662 697 A1.
An object of the invention is to provide a method and apparatus of the initially mentioned type for controlling an electromagnetically operable valve, with low-wear and low-noise, while ensuring a secure capturing of the valve element by the solenoid.
Another object of the invention is to provide such a method and apparatus which, in particular, are suitable for variable valve timing in the case of internal-combustion engines.
These and other objects and advantages are achieved by the valve control method according to the invention, in which the impact velocity is controlled to a minimal value. For this purpose, the switch-on point in time of the capturing current pulse is determined based on the gradient of the impact velocity, and can be varied to achieve a minimal impact velocity. This approach is based on the recognition that, if the switch-on point of the capturing current pulse is varied while the parameters otherwise remain the same, the impact velocity curve passes through a minimum.
The present invention automatically adjusts the valve operation to achieve the minimal impact velocity by adjusting the the pertaining switch-on point to a value, which in the following will be called "optimal", for the capturing current pulse. This is achieved by an iterative process in which the switch-on time for a next capture of the valve element is determined from the previous switch-on point, by the addition of a control increment which is defined as a minimum target function dependent on the above-mentioned velocity gradient. In this case, the minimum target function is any function which changes the switch-on point for the capturing current pulse toward the optimal target value which leads to the minimal impact velocity. This includes particularly functions with a negative zero crossing; that is, in which the gradient curve extends with a negative ascent through the coordinate zero point. This ensures that the control will always find the operating point of minimum impact velocity for the life of the valve, independently of possibly variable interference influences, such as friction or temperature. A storage and operation-dependent modification of characteristic diagrams for the diverse parameters of the valve control is therefore not absolutely necessary for this purpose.
According to a feature of the invention, the functional dependence of the control increment on the velocity gradient is specially selected so that, on the one hand, it can be implemented and constructed at low expenditures and, on the other hand, it permits a fast reaction of the control to deviations from the minimal impact velocity.
According to another feature of the invention, the impact velocity is advantageously obtained from a time-dependent measurement of the valve element operating path. For this purpose, a corresponding valve element path sensor system is provided. In this manner, the impact velocity can be determined with reasonable precision.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.